Simple question-worth is a PowerBreathe the money?
If you can stop laughing at what it looks like
less than £20 instead of £50 changes the it might make a difference equation. I have one and used it regularly for about 3 months and it seemed to help my climbing, of course over the 3 months I did lots of climbing too so would have got better anyway.
Bottom line is it isn't running, swimming or cycling so it doesn't get done anymore whether it might help or not.